Valiant VFO Resistor

[David C. Hallam]

Can I assume that this applies to the VFO in the Pacemaker also?  I would
think changing to a 6BH6 would be a better choice than the 6AH6.

David
KC2JD/4

> -----Original Message-----
> From: Boat Anchor Owners and Collectors List
> [mailto:BOATANCHORS at LISTS.TEMPE.GOV]On Behalf Of Glen Zook
> Sent: Tuesday, November 18, 2008 3:42 PM
> To: BOATANCHORS at LISTS.TEMPE.GOV
> Subject: Re: Valiant VFO Resistor
>
>
> The consensus is that the resistor should be inside the VFO box.
> This is because the temperature compensating was done by Johnson
> with the resistor inside.  As such, it actually takes much longer
> for the VFO to stabilize if the resistor is not inside.  There
> have been several amateur radio operators who have researched
> this (by experimentation) and have decided that it is best to
> leave the resistor inside the VFO compartment.
>
> Now the original resistor definitely does not have enough power
> dissipation and therefore definitely needs to have a higher rating.
>
> Like the Heath VF-1 and DX-100 series VFOs, the VFO in the
> Ranger, Valiant, etc. can be stabilized more by a few changes.
> The first is to change the tube from a 6AU6 to a 6AH6.  This is a
> direct replacement and the only thing that might be required is
> to "touch up" the trimmer capacitors (only) because the inter
> electrode capacitance of the tubes are slightly different.  This
> single "modification" makes "light years" difference in the stability.
>
> The second is to change the 0A2 voltage regulator to an 0B2.
> This drops the screen voltage from 150 volts to 108 volts which
> definitely helps stabilize the oscillator.
>
> The third thing is to modify the B+ to the oscillator by
> regulating it down from the 300+ to 150 volts.  Using the 0A2
> removed from the screen circuit is a good place to use that
> regulator tube.
>
> Doing these 3 things will make a noticeable improvement in the
> stabilization of the VFO frequency.
>
> Glen, K9STH
>
> Website:  http://k9sth.com
>
>
> --- On Tue, 11/18/08, hudlerb1 at netzero.com <hudlerb1 at NETZERO.COM> wrote:
>
> > From: hudlerb1 at netzero.com <hudlerb1 at NETZERO.COM>
>
> There has been some controversey over whether this 18K VR
> dropping resistor should be inside or outside the VFO box.
>
> One thought, if it is out of the box, it keeps the VFO from
> heating as much, thus less drift.
>
> Another is if it is under the chassis, it never warms completely
> over a long time, thus drifts slower but never reaches operating temp.
>
> 5 or 10 watt resistor?
>
> I'm getting back into my rig to finish the mods, calibrate again,
> and get it back on 160 very soon.
>
>
>
>
> -----------------------------------------------------------
> This list is a public service of the City of Tempe, Arizona
> -----------------------------------------------------------
>
> Subscription control -
> http://www.tempe.gov/lists/control.aspx?list=BOATANCHORS
> To post - BOATANCHORS at LISTS.TEMPE.GOV
> Archives - http://lists.tempe.gov/archives/BOATANCHORS.html
>

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.aspx?list=BOATANCHORS
To post - BOATANCHORS at LISTS.TEMPE.GOV
Archives - http://lists.tempe.gov/archives/BOATANCHORS.html